Description
Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
Note: For the purpose of this problem, we define empty string as valid palindrome.
Constraints
s consists only of printable ASCII characters.
Approach
Links
Examples
Input: "A man, a plan, a canal: Panama"
Output: true
Input: "race a car"
Output: false
Solutions
/**
* Time complexity : O(N)
* Space complexity : O(1)
*/
class Solution {
public boolean isPalindrome(String s) {
if(s == null || s.length() < 2) return true;
for(int i = 0, j = s.length()-1; i < j; i++, j--) {
while(i < j && !Character.isLetterOrDigit(s.charAt(i))) {
i++;
}
while(i < j && !Character.isLetterOrDigit(s.charAt(j))) {
j--;
}
if(i < j) {
if(Character.toLowerCase(s.charAt(i)) !=
Character.toLowerCase(s.charAt(j))) {
return false;
}
}
}
return true;
}
}
Follow up